1. FIELD OF THE INVENTION
The present invention relates to a control system for tracking a moving object and for training a device to lead the object. In a particular adaptation, the present invention relates to a fire control system for optically tracking a moving object and for training a gun such that a projectile fired therefrom will hit the object.
2. DESCRIPTION OF THE PRIOR ART
Gun fire control systems operate, in general, by first determining the kinematic characteristics of a moving target, then calculating a firing offset angle displaced from a datum line, defined as the direct line of sight from the gun to the target and finally training the gun so as to lead the moving target by this offset angle. The kinematic characteristics of the target used by a fire control system include the target distance measured by the displacement tangential velocity or speed across the line of sight and the angular speed of the target relative to the gun. The speed across the line of sight is the speed vector component of the velocity of the target resolved in a direction perpendicular to the datum line.
The quantities required by a fire control system to calculate the firing offset angle include the ballistic parameters of the gun and the projectile fired therefrom. If the gun is mounted on a moving vehicle, such as a tank, the calculation of the firing offset angle also involves the speed and direction of the vehicle. The ballistic parameters of the projectile are used in combination with the target distance to calculate the travel time of the projectile to the target and ultimately to calculate the firing offset angle.
The target speed across the line of sight and the angular speed of the target vary with time. Consequently, it is advantageous to automatically and continuously determine the angular speed of the target and the firing offset angle. One method of obtaining the angular speed of the target is by visually following the target with a telescope and determining the angular speed of the telescope.
The particular method used in calculating and inserting the firing offset angle depends upon the specific fire control system. In many fire control systems, the firing axis of the gun, which in these systems is also the datum line, is normally kept parallel to the optical axis of the telescope. Hence, as the target is tracked with the telescope, the gun is also kept on the target. These systems use at least two methods for inserting corrections such as the firing offset angle. One method automatically offsets the telescope optical axis in a manner well known in the art to lag the target by an angle equal to the firing offset angle. The telescope operator, who has been tracking the target, then realigns the optical axis of the telescope onto the target image by operating the gun positioning mechanism, the telescope thereby also being realigned by an equal angular amount. Hence, the result is that the gun leads the target by the desired firing offset angle. The other method for inserting the firing offset angle uses a more sophisticated approach. In this method, the firing control system automatically offsets the firing axis of the gun, and hence the datum line, to lead the target by an angle equal to the calculated firing offset angle. The system simultaneously offsets the optical axis of the telescope to lag the datum line by an angle equal to the firing offset angle. Consequently, if the firing offset angle has been correctly calculated the optical axis of the telescope is exactly aligned to the target image.
Most of the fire control systems presently using the above methods utilize a computer for generating analog signals, that is, signals which vary continually with time. The analog signals are used to operate either electro-mechanical or electro-hydraulic servo systems for the gun and telescope. These fire control systems have proven to be complicated, overly delicate, and expensive. Furthermore, these systems are sensitive to variations in temperature which cause undesirable changes in the critical timed sequencing of the system components.
Other systems having sighting and aiming servo systems include laser beam systems used in the field of celestial telemetry. Because of the appreciable time required for the electromagnetic radiation to reach the distant celestial objects, it is necessary to accurately and smoothly offset the laser firing axis to a point ahead of the celestial object. Present sighting and aiming servo-systems usually do not provide either the requisite accuracy or the desired smoothness of operation.